Just picked up a pair of these. I am quite pleased with them. Having recently gotten on the Compression socks band wagon I was interested to see if compression tights would have similar benefits.
What I first noticed wearing them was a sense that my muscles and joints were supported. Not dramatically, just very comfortable. This was consistent throughout.
They do, and are supposed to, fit very snuggley. While running they quickly became unnoticable.
Talking to my physiotherapist, he had mentioned that the biggest benefit from these tights is most likely physchological. Not in the normal, I look fast so therefore I am, phsychological, but more in the fact that the compression gives the body more/constant feedback than not wearing them. This apparently keeps the brain focused on maintaining proper form. This can lead to less injuries, especially for distance runners, when your form starts to deteriorate on longer runs when you get fatigued.
But, most important of all, is that they look bad ass!! You look like some sort of hybrid machine/human combo. Definetely a big intimidation factor at the start line!
Definetely worth trying out!